Many of those people aren't bothered about bronze aged ideas about powerful spirits, though, Hope. They're concerned with the culture and society in which they live, a culture which views marriage as the basis of a family, as something to aspire to.
Oh, I quite agree, O. That is why I said what I said. As a Christian, I'm not
bothered about bronze aged ideas about powerful spirits
; I'm concerned about the day-to-day life of the late 20th/early21st Century, a period of time that I understand God to intimately involved in.
You may not think he is, and that's your prerogative, but then not everythin you think or belief is necessarily correct.
Marriage means different things to different people, and the law defines the minimum standards of what it entails in terms of legal entitlements, tax allowances, obligations and freedoms in court testimony and parental access and the like. Society the interprets that - and any changes in it - and exerts a social pressure based on the idea of marriage.
Precisely, O. Society, through its laws, "defines the minimum standards of what it entails in terms of legal entitlements, tax allowances, obligations and freedoms in court testimony and parental access and the like". That's just another way of saying what I said. There are, of course, those who regard those 'minimums' as just that, minimalist, and seek to life to a higher 'minimum' level.
That's not a purely religious thing, although it can have religious overtones, and within some subcultures - say the Christian community - that religious element can be emphasised, but it's neither intrinsic nor necessary.
Except that marriage was always first and foremost a religious, as opposed to a civil, contract. The balance has only changed in the last 2-300 years here in the West.
Marriage as a concept predates Christianity, ...
I'm glad you've realised that - but have you also understood that it predates 'civil society'
... and as a word is as open to reinterpretation to take it away from a purely religious view as it was to reinterpretation by the religious whilst it was a purely religious concept.
I'm not convinced that civil society can amend the meaning of a term that long predates it as easily as you think. Perhaps you ought to consider whether civil society can amend the idea of 'law' (another concept that long predates the concept of civil society) as easily as that.